AAPG Bulletin, V. 83 (1999), No. 7 P. 1119-1134.

The Magneto-Susceptibility Event and Cyclostratigraphy (MSEC) Method Used in Geological Correlation of Devonian Rocks from Anti-Atlas Morocco¹

Brooks B. Ellwood,² Rex E. Crick,² and Ahmed El Hassani³

©Copyright 1999.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received July 8, 1996; revised manuscript received January 26, 1998; final acceptance December 8, 1998.
²Department of Geology, Box 19049, The University of Texas at Arlington, Arlington, Texas 76019-0049.
³Institut Scientifique, Département Géologie, Avenue Ibn Batouta, B.P. 703 Rabat - Agdal, Morocco.
 

Funding for sampling in Morocco was provided by grants from NSF, EAR-9219489 to Crick, and EAR-9628202 to Crick and Ellwood, and by the American Chemical Society, Petroleum Research Fund (Grant 30845-AC8) to Crick and Ellwood. We are especially grateful for logistic support provided by the Institut Scientifique, Rabat, Morocco, and permission to remove samples for analysis. Several members of the Subcommission on Devonian Stratigraphy (Thomas Becker, Pierre Bultynck, Michael House, Otto Walliser) were extremely helpful by supplying details of unpublished measured sections and difficult-to-obtain publications. Thomas Becker, Michael House, and Otto Walliser unselfishly took time from their own field work in the Tafilalt to provide details of correlation. We are grateful to Sue Ellwood for her help in the field and dedication in sample preparation and measurement. We would like to thank Wolf Gose (University of Texas at Austin) for use of his cryogenic magnetometer for the paleomagnetic data reported in Figure 5. The Department of Geology and College of Science at University of Texas at Arlington is also gratefully acknowledged for its financial support. 

ABSTRACT

Magneto-Susceptibility Event and Cyclostratigraphy (MSEC) is used here as a means of establishing sensitive chronostratigraphic markers and chronohorizons useful for high-resolution correlation. MSEC is a composite of the magnetic susceptibility (MS) record of marine strata and the coeval biostratigraphic record and, similar to chronozones, zones based on MSEC data have boundaries that are isochronous. MS, a measure of the concentration of magnetic grains in sediments, proxies for the ratio of lithogenic to biogenic components. Controls on the detrital input of lithogenic material include eustasy and climate, however induced, and sea floor/basin subsidence. The development of an initial MSEC composite reference curve for the Middle-Upper Devonian of the Anti-Atlas region of southern Morocco is presented and discussed in the context of global sea level transgressive and regressive cycles. MSEC trends, composed of increasing MS magnitudes, correlate well with episodes of regression, whereas trends of decreasing MS magnitudes correlate with episodes of transgression.